The present invention relates to the improvement of magnetic recording media and more particularly to the magnetic recording media for the high frequency wave recording suitable for the requirement of magnetic recording in ultrahigh density which is higher in density than the recording in ordinary video signals and audio signals.
For the purpose of raising the recording density and the sensitivity of the magnetic recording medium, the support base has been coated with a magnetic layer comprising a binder containing dispersed ferromagnetic powder whose squareness ratio (i.e., residual magnetic flux density Br/saturation magnetic flux density Bm) is great and both Br itself and coercive force Hc are great. For the requirement of both squareness ratio and Hc, in this case, iron oxide type magnetic powder such as cobalt adsorbed .gamma.-Fe.sub.2 O.sub.3 and metallic magnetic powder such as Fe and Fe--Co--Ni are utilized as ferromagnetic powder to be contained in a magnetic layer. Especially, it is deemed that metallic magnetic powder are suitable for the ferromagnetic powder whose squareness ratio and Hc are great. Hc of these metallic magnetic powder is usually 1000 Oe or so (900-1200 Oe) which has not been suitable for the high frequency wave recording of the density required in ordinary video signals and audio signals.
However, when the recording which is higher in density than the aforesaid high frequency wave recording is required e.g., for 8 mm video, a magnetic recording medium whose Hc does not exceed the aforesaid 1000 Oe or so by much is easily disturbed and making it difficult to maintain the recording because repeated signals are constantly given to the recording medium in an ON/OFF mode. Further, the aforesaid ferromagnetic powder are acicular crystals and the length of a major axis thereof is 0.3-0.9.mu., the length of a minor axis is 0.05-0.1.mu. and an acicular ratio Ra (i.e., major axis/minor axis ratio) is thereby from 5 to 10 which is very large. Therefore, if the ferromagnetic powder is finely granulated to obtain a high Hc, it becomes brittle and the Hc varies in the magnetic layer, which causes the magnetic transferring for stacking. Meanwhile, due to the requirement of raising the degree of orientation in the ferromagnetic powder having a high acicular ratio, the more the powder is finely granulated, the greater is the orientating magnetic field which is needed and thereby the surface of the magnetic layer becomes rough, the saturation magnetic flux density Br becomes small and thereby the recording medium is easily saturated, thus the ferromagnetic powder having a high acicular ratio is not suitable for a recording having high sensitivity, high output and high density.